1. Field of the Invention
The present invention relates to an internet protocol (IP) switch using an asynchronous transfer mode (ATM) switch in a switch section.
2. Description of the Related Art
A prior art IP switch is constructed by a controller and a switch section.
The operation of the prior art IP switch is as follows.
Initially, a connection from a first node via the IP switch to a second node is established by an initial path controlled under the controller. Then, after a predetermined time has passed, the initial path is replaced by a selected flow connection. In the selected flow connection, a logical IP connection from the first node via the switch section to the controller and a logical IP connection from the controller via the switch section to the second node are established.
Further, after another predetermined time has passed, the selected flow connection is replaced by a cut through connection, thus releasing the load of the controller. Note that the cut through connection is connected directly between the two nodes and without passing through the controller. This will be explained later in detail.
In the above-described prior art IP switch when the selected flow connection is replaced by the cut through connection, the connection between the two nodes may be disconnected for some time. As a result, if there are cells input to the IP switch during that time, such cells are discarded.
It is an object of the present invention to provide an IP switch capable of avoiding the scrapping of cells during a transition time from a selected flow connection to a cut through connection.
According to the present invention, in an IP switch including a controller and a switch section controlled by the controller, the switch section includes an input cell buffer for receiving cells input to the switch section. The output of the input cell buffer is closed during a transition time from a selected flow connection linked to the input cell buffer and the controller, to a cut through connection linked to the input cell buffer without linking to the controller. Then, after the cut through connection is established, the output of the input cell buffer is opened.
Since cells that reached the IP switch during the above-mentioned transition time are stored in the input cell buffer, such cells are never discarded. Therefore, it is unnecessary to retransmit cells between the nodes using an upper layer. As a result, the traffic efficiency can be enhanced.